I. Field of the Invention
This invention relates to the fields of cellular biology and membrane and protein biochemistry. In particular, the present invention provides fusion proteins encoding fluorescent proteins. The fusion proteins target glycolipid-enriched membrane (GEM) and non-glycolipid-enriched membrane (non-GEM) domains of cell membranes by virtue of membrane-anchoring signal from p56lck or pp60c-src, respectively.
II. Background
The plasma membrane of mammalian cells contains domains representing distinct regions within the lipid bilayer with a composition that is different from the bulk composition of the plasma membrane. An important example of such domains are glycolipid-enriched membrane (GEM) domains (Simons and Toomre, 2000), also referred to as lipid rafts. Besides glycolipids, GEM domains are enriched with cholesterol and specific proteins, many of which function in cell signaling. The enrichment of signaling proteins in GEM domains has led to the notion that they represent a specialized signaling compartment within the plasma membrane. Importantly, recent studies corroborate this hypothesis. For example, in T cells, disruption of GEM domains also inhibits T cell activation (Xavier et al., 1998)
Despite the current interest in GEM domains, many of their properties remain elusive. This is due in part to the fact that many studies of GEM domains include detergent lysis of cells in order to separate the detergent-resistant GEM fraction from the non-GEM fraction of the plasma membrane. Obviously, such procedures are highly disruptive and, in addition to potentially altering the natural structure of such domains, the permit no follow-up experiments to explore further functional aspects. Thus, there remains a need to develop new and improved methods for examining GEM and non-GEM targeting in situ.